Car: 2005 Outback L Automatic Pertinent Modifications: Description of the problem: P0131... please don't jump to conclusions here. Recent maintenence or modifications: PO replaced 2.5 (ej253) with 2.0 (ej203) Alright, so I picked up this outback knowing it was throwing an O2 CEL. I ran to the auto store and grabbed a scanner and found P0131 (front O2 volt low). On my way out, I snagged a replacement front O2 and jacked the car up to find the current O2 sensor looks pretty new (hardly any grime on it). So I returned the O2 I got because I wanted to investigate this before fighting the old one out (side note, WTF Subaru, why did you make the front O2 so hard to get out of the N/A cars?). Anyways, I borrowed a Tactrix cable thinking it might be related to the displacement and pulled a few logs and was pretty surprised to find that the front O2 seems to work fine for the first few minutes of the drive. I reset the ECU (clearing p0131) and left for a drive. Everything seems fine until I let off the throttle going down a hill and the AFR in the logs ramps from ~15-16 (seemingly normal afr for closed throttle) all of the way to 20.44 within a 200 ms. It sits at 20 aft for about 2500 ms before switching straight to 14.7... Sometime during this time period, the car will trip P0131. What is weird is that if I turn the key off and back on quickly, the O2 sensor starts reading the correct values again (despite P0131 staying thrown). It will work fine for almost a minute before it goes back to 14.7 while driving. To me it seemed like it was a physical issue with the wire except it works immediately after a key cycle. I tugged on the wires but didn't see a change when the ECU reads 14.7. I also thought it could be a failing o2 but the PO mentioned it was recently replaced by the owner before him (accurate based on what I saw under the car) to attempt to fix the same code. I don't know if the ECU shuts power off to the O2 when It thinks its bad, but that seems to be happening in this case. Anywho, I am going to do some research on this but wanted to see if anyone had any issues like this before. I'm trying not to throw money at it and the front O2 is too expensive and much of a PITA to replace on a whim.